1. Field of the Invention
The invention relates to a heating process of the light irradiation type in which the article to be treated is heat-treated by light irradiation of the article to be treated using a heating device of the light irradiation type.
2. Description of Related Art
In semiconductor production, heat treatment is generally used for different processes such as film formation, oxidation diffusion, diffusion of impurities, nitriding, film stabilization, silicide generation, crystallization, ion implantation activation and the like.
To improve yield and quality in semiconductor production, rapid thermal processing (RTP) is desirable, in which the temperature of the article to be treated, such as a semiconductor wafer or the like, is rapidly raised or lowered. In RTP, a heat treatment device of the light irradiation type using light irradiation with a light source such as a filament lamp or the like is widely used.
A filament lamp in which there is a filament within the bulb of transparent material, is a typical lamp in which light can be used as heat since, in this connection, greater than or equal to 90% of the input power is radiated, and since heating is possible without contact with the article to be treated.
In the case of using such a filament lamp as the heat source for heating a glass substrate and a semiconductor wafer, the temperature of the article to be treated, compared to a resistance heating process, can be raised/lowered more rapidly. This means that the temperature of the article to be treated can be increased, for example, to at least 1000° C. in a few seconds to a few dozen seconds by heat treatment of the light irradiation type. After light irradiation has been stopped, the article to be treated is rapidly cooled. This heat treatment of the light irradiation type is normally performed several times.
If, in this connection, the article to be treated is, for example, a semiconductor wafer of monocrystalline silicon, when the semiconductor wafer is heated to at least 1050° C., if in the temperature distribution of the semiconductor wafer a nonuniformity appears, there is a possibility that in a semiconductor wafer a phenomenon called slip, i.e., a defect of crystal transition, arises, resulting in that inferior goods will be formed. Therefore, when RTP of the semiconductor wafer is performed using a heat treatment device of the light irradiation type, heating, holding at a high temperature and cooling must be performed in such a way that the temperature distribution on the entire surface of the semiconductor wafer becomes uniform. This means that, in RTP, there is a demand for very accurate temperature uniformity of the article to be treated. One example of a conventional heating device of the light irradiation type with consideration of the temperature uniformity of the article to be treated in heat treatment is described in Japanese patent disclosure documents JP SHO 62-20308 A and JP SHO 63-260127 A which corresponds to U.S. Pat. No. 4,859,832.
In the heating device of the light irradiation type of JP SHO 62-20308 A, the heating means is a light irradiation means formed, for example, of several halogen lamps arranged parallel to one another. These halogen lamps are divided into groups of a few lamps, each group is assumed to be a unit of control and the heat output from each group is controlled independently of one another. The temperature of several points of the article to be treated is detected with a radiation thermometer and the above described unit of control is controlled based on this detection result such that the temperature of the article to be treated becomes uniform.
In the heating device of the light irradiation type of JP SHO 63-260127 A and U.S. Pat. No. 4,859,832, the heating means is a light irradiation means formed, for example, of several annular infrared lamps of different diameters that are arranged concentrically with respect to each other. The controller of this heating device of the light irradiation type determines data beforehand of the type of lighting control of the IR lamps required to make the temperature distribution of the article to be treated uniform to a given temperature for the given the different temperature distribution patterns of the article to be treated. Thus, a tabular outline of the “Patterns of the respective temperature distribution against patterns of lighting control of IR lamps” is stored.
During heat treatment, at least two points of the article to be treated are measured with a radiation thermometer, and the patterns of the temperature distribution are determined. The controller finds the pattern of the temperature distribution as near as possible to the measured pattern of the temperature distribution from the stored tabular outline and controls the IR lamps, as the heating means, based on the pattern of lighting control of the IR lamps which corresponds to the most similar pattern of the temperature distribution, so that the temperature of the article to be treated becomes uniform.
The light irradiation means serving as the heating means of the heating device of the light irradiation type described in Japanese patent disclosure document JP 2002-203804 A and corresponding U.S. Pat. No. 6,876,816 has a first lamp unit and a second lamp unit. In the first lamp unit, there are several U-shaped, double-end lamps arranged in the parallel and perpendicular directions with respect to the page of drawings, in which there are feed devices for the filaments on the two ends of the bulb. In the second lamp unit, there are several straight, double-end lamps arranged in perpendicular directions with respect to the page of drawings, in which there are feed devices for the filaments on the two ends of the bulb. The second lamp unit is located underneath the first lamp unit. The article to be treated is heated by the light irradiation to the article to be treated, such as a semiconductor wafer or the like which is located underneath the above described second lamp unit.
In the heating process described in JP 2002-203804 A (U.S. Pat. No. 6,876,816), the heating region of the semiconductor wafer as the article to be treated is divided into several zones which are centrosymmetric 1 and concentric. By combining the distribution of light intensities of the respective lamps of the first and second lamp units with one another, synthetic light intensity distribution patterns are formed which correspond to the respective zone and which are centrosymmetric to the middle of the semiconductor. Thus, heating is performed according to the temperature change of the respective zone measured with the radiation thermometer. In this connection, the semiconductor wafer which constitutes the article to be treated is turned to suppress the effect of variations of the illuminance of the radiation of the lamps. This means that the respective, concentrically arranged zone can be heated at an individual illuminance.
In Japanese patent disclosure document JP HEI 3-218624 A (JP 2940047 B2), a device using single-end type halogen lamps is described in which, according to the thermal radiation characteristic of the respective part of the article to be heated, the amount of IR irradiation of the lamps which are opposite the respective part is set such that the amount of heat radiation thereof is supplemented.
For all heat treatments of the light irradiation type which are described in the above described publications, the temperature of the article to be treated is monitored and the emission of the lamps of the heating means of the light irradiation type is controlled based on the monitoring result, such that the temperature of the article to be treated becomes uniform. Therefore, for example, even in the vicinity of the edge area of the article to be treated, which is in contact with the treatment table which supports the article to be treated and in which a temperature drop often occurs by heat radiation, by controlling the emission intensity of the lamps which correspond to the edge area, a constant temperature distribution of the article to be treated can be accomplished.
However, it has been found that, in the above described conventional heating devices of the light irradiation type, the following disadvantages occur.
When the article to be treated is a semiconductor wafer, for example, generally, a film of metal oxide, metal nitride or the like is formed on the surface of semiconductor wafer by sputtering on or the like or impurities additive are doped by ion implantation. In this connection, local distributions on the wafer surface are formed in the surface conditions of the semiconductor wafer by film formation or in the density of the dopant ions which are implanted in the ion implantation process. These distributions are not always centrosymmetric relative to the center of the semiconductor wafer, but rather are asymmetrical to the center of the semiconductor wafer. When a distribution of the surface conditions of the semiconductor wafer arises, a distribution of emissivity on the semiconductor wafer surface is formed. The amount of light absorption of the material which is irradiated with light depends on the emissivity of the material. The temperature of the semiconductor wafer therefore has a local distribution even if, for example, irradiation and heating are performed with light such that the surface of the semiconductor wafer has a uniform intensity distribution.
The factor of formation of the above described local distribution of the surface properties of the semiconductor wafer results from, for example, different film types being formed on the surface of the semiconductor wafer. If, for example, a case is imagined where the semiconductor wafer is formed of monocrystalline silicon, according to the construction of the semiconductor device in the region of the surface of the semiconductor wafer, a SiO2 film is formed, while in another area thereof, a SiN film is formed and in a still further area, no film is formed. If the types of locally formed films differ in this way, the emissivity differs in each film formation area.
Furthermore, for example, even for the same film type, according to the film formation conditions in one region a dense film with a mirror-like surface is formed, while in another region a film is formed with a porous surface. Even if only these surface conditions of the film differ from one another, the emissivities differ from one another.
On the other hand, the emissivities differ from one another in the same way as in the above described different surface conditions of the semiconductor wafer, when the dopant ion density in the surface layer of the ion implanted workpiece in the ion implantation process differs. This means that, according to the local distribution of the density of dopant ions on the semiconductor wafer surface, a local distribution of emissivity occurs. As in the above described case of the presence of a distribution of surface conditions of the semiconductor wafer, the semiconductor wafer temperature has a local distribution even if, for example, irradiation and heating are performed with light such that the surface of the semiconductor wafer has a uniform light intensity distribution.
In the heating device of the light irradiation type described in JP SHO 62-20308 A and JP SHO 63-260127 A (U.S. Pat. No. 4,859,832), in each case, the light irradiation means as the heating means are arranged symmetrically to one another. In the heating device of the light irradiation type described in JP SHO-62-20308 A, groups of a few halogen lamps that are the units of the control are arranged centrosymmetrically. In the heating device of the light irradiation type described in JP SHO 63-260127 A (U.S. Pat. No. 4,859,832), the light irradiation means is arranged such that several annular IR lamps with different diameters are concentrically arranged.
Therefore, the distribution pattern of the light intensity on the article to be treated can be established only symmetrically to its shape, even if according to the temperature distributions which have been measured and obtained with a radiation thermometer at several points, lighting control of the respective lamp is attempted. Therefore, in practice it is difficult to heat-treat an article to be treated like the above described semiconductor wafer with a temperature property asymmetrical to the shape of the article to be treated, with a uniform temperature.
On the other hand, in the heating device of the light irradiation type described in JP 2002-203804 A (U.S. Patent Application Publication 2004/0112885 A1), for light irradiation, as the heating means there are several U-shaped, double-end lamps, in which on the two ends of the bulbs there are feed devices for the filaments, arranged parallel and perpendicular to the page of the drawings, synthetic light intensity distribution patterns which are centrosymmetric to the center of the semiconductor wafer are formed which correspond to the respective concentric zones as the heating region of the semiconductor wafer and are centrosymmetric to the center of the semiconductor, and heating is performed according to the temperature distribution of the respective zone.
But since the above described synthetic light intensity distributions are centrosymmetric relative to the center of the semiconductor wafer and since the semiconductor wafer is itself turning, as a result, in practice, it is difficult to heat-treat an article to be treated with a temperature property asymmetrical to its shape, with a uniform temperature.
In the heat treatment of the light irradiation type described in all the aforementioned publications, a radiation thermometer is used in each case for temperature measurement. Assuming that the temperature of the measured object is the same at each point, the same temperature is shown when the emissivity of the measurement points is the same. However, if the article to be treated is a semiconductor wafer, as was described above, the semiconductor wafer has a local distribution of emissivity. Even if the true temperature of the wafer were to be, for example, uniformly at 1050° C., due to the different emissivities, certain points have a measured value of 1055° C. and other points have a measured value of 1045° C., etc. Therefore, the lamp control system which is connected to the respective radiation thermometer, due to the above described apparent measurement result, carries out control with feedback so that, if control is set to uniform control at 1050° C., for example, the lamp control system which corresponds to points with 1055° C. reduces the power supplied to the lamp, while the control system which corresponds to the points with 1045° C. increases the power supplied to the lamp, so that in this way control is exercised such that the apparent temperature measurement value of the respective radiation thermometer is set to 1050° C. As a result, the real temperature of the points with lower emissivity becomes high and the real temperature of the points with a higher emissivity becomes low. This means that, during heat treatment, a temperature distribution is formed, and under certain circumstances, there is a possibility that slip will occur in the semiconductor wafer, and thus, inferior goods will be formed.
In the heat treatment of the light irradiation type described in the aforementioned publications, in any case, the purpose is to make the temperature of the article to be treated uniform in heat treatment. Therefore, when this heat treatment is performed, the following disadvantages can occur.
When the article to be treated is, for example, a semiconductor wafer, generally, as was described above, impurities additive are doped on the surface of the semiconductor wafer by ion implantation, and the local distribution of the density of dopant ions on the surface of the semiconductor wafer is asymmetrical to the center of the semiconductor wafer.
If, in this connection, based on the conventional heat process, the semiconductor wafer is heated and activated such that the temperature of the article to be treated is uniform, according to the distribution of the density of dopant ions, a distribution also occurs in the carrier concentration. This means that the points with a high density of dopant ions have a higher carrier concentration and a lower sheet resistance value. On the other hand, the points with the low density of dopant ions have a lower carrier concentration and a higher sheet resistance. The local electrical property of the semiconductor wafer therefore varies, by which it becomes difficult to obtain a uniform electrical property.
In the case of film formation by heating the surface of the semiconductor wafer, film formation is performed by heating the semiconductor wafer by light irradiation by allowing a raw gas to flow as the film material on the surface of the semiconductor wafer. In this connection, the distribution of the gas flow of the raw gas on the surface of the semiconductor wafer is not uniform. If, in this state, the semiconductor wafer is heated with a conventional heat process and thus film formation is accomplished such that the temperature of the article to be treated is uniform, therefore a local distribution occurs in the composition of the film formed on the semiconductor wafer and in its film thickness. As a result, variations of the electrical property of the semiconductor wafer, and consequently, variations in the device characteristic occur.
The above described disadvantages are difficult to eliminate by conventional heat treatment which is intended to make the temperature of the article to be treated uniform.